- Index
- Preface
- Product Overview
- Command-Line Interfaces
- Configuring the Switch for the First Time
- Administering the Switch
- Configuring Interfaces
- Checking Port Status and Connectivity
- Configuring Supervisor Engine Redundancy Using RPR and SSO
- Configuring NSF with SSO Supervisor Engine Redundancy
- Configuring In Service Software Upgrade Process
- Configuring Control Plane Policing
- Environmental Monitoring and Power Management
- Configuring Power over Ethernet
- Configuring Switches with Cisco Network Assistant
- Configuring VLANs, VTP, and VMPS
- Configuring IP Unnumbered Interface
- Configuring Layer 2 Ethernet Interfaces
- Configuring SmartPort Macros
- Configuring STP and MST
- Configuring Optional STP Features
- Configuring EtherChannel
- Configuring IGMP Snooping and Filtering
- Configuring 802.1Q and Layer 2 Protocol Tunneling
- Configuring CDP
- Configuring UDLD
- Configuring Unidirectional Ethernet
- Configuring Layer 3 Interfaces
- Configuring Cisco Express Forwarding
- Configuring IP Multicast
- Configuring Policy-Based Routing
- Configuring VRF-lite
- Configuring QoS
- Configuring Voice Interfaces
- Configuring 802.1X Port-Based Authentication
- Configuring Port Security
- Configuring DHCP Snooping and IP Source Guard
- Configuring Dynamic ARP Inspection
- Configuring the AGM for the First Time
- Configuring Network Security with ACLs
- Configuring Private VLANs
- Configuring Port Unicast and Multicast Flood Blocking
- Configuring Port-Based Traffic Control
- Configuring SPAN and RSPAN
- Configuring System Message Logging
- Configuring SNMP
- Configuring NetFlow
- Configuring RMON
- Performing Diagnostics on the Catalyst 4500 Series Switch
- Configuring WCCPv2 Services
- Configuring MIB Support
- ROM Monitor
- Acronyms
Port Unicast and Multicast Flood Blocking
This chapter describes how to configure multicast and unicast flood blocking on the Catalyst 4500 series switch. This chapter contains these topics:
Note For complete syntax and usage information for the switch commands used in this chapter, refer to the Catalyst 4500 Series Switch Cisco IOS Command Reference and related publications at this location:
http://www.cisco.com/univercd/cc/td/doc/product/software/ios124/124cr/index.htm.
Overview of Flood Blocking
Occasionally, unknown unicast or multicast traffic is flooded to a switch port because a MAC address has timed out or has not been learned by the switch. (This condition is especially undesirable for a private VLAN isolated port.) To guarantee that no unicast and multicast traffic is flooded to the port, use the switchport block unicast and switchport block multicast commands to enable flood blocking on the switch.
Note The flood blocking feature is supported on all switched ports (including PVLAN ports) and is applied to all VLANs on which the port is forwarding.
Configuring Port Blocking
By default, a switch floods packets with unknown destination MAC addresses to all ports. If unknown unicast and multicast traffic is forwarded to a switch port, there might be security issues. To prevent forwarding such traffic, you can configure a port to block unknown unicast or multicast packets.
Note Blocking of unicast or multicast traffic is not automatically enabled on a switch port; you must explicitly configure it.
Blocking Flooded Traffic on an Interface
Note The interface can be a physical interface (for example, GigabitEthernet 1/1) or an EtherChannel group (such as port-channel 5). When you block multicast or unicast traffic for a port channel, it is blocked on all ports in the port channel group.
To disable the flooding of multicast and unicast packets to an interface, perform this task:
This example shows how to block unicast and multicast flooding on a GigabitEthernet interface1/1 and how to verify the configuration:
Switch# configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Switch(config)# interface gigabitethernet1/1
Switch(config-if)# switchport block multicast
Switch(config-if)# switchport block unicast
Switch(config-if)# end
Switch# show interface gigabitethernet1/1 switchport
Name: Gi1/3
Switchport: Enabled
<output truncated>
Port Protected: On
Unknown Unicast Traffic: Not Allowed
Unknown Multicast Traffic: Not Allowed
Broadcast Suppression Level: 100
Multicast Suppression Level: 100
Unicast Suppression Level: 100
Resuming Normal Forwarding on a Port
To resume normal forwarding on a port, perform this task: